Crisp rice is a product frequently used in the manufacture of crisp candy bars, cookies, granola bars and other snacks and confections in addition to its well known use as a breakfast food.
A typical crisp rice process is an oven-puffing process which begins with whole kernels of rice. The rice kernels are first cooked in a retort for several hours together with sugar, salt and malt. The cooked kernels are then dried to a moisture content of 25% to 30%, tempered for about 15 hours to equilibriate moisture, and dried again to a moisture content of 18-20%. The dried kernels are then radiantly heated to plasticize the outside layers of the kernel, "bumped"0 on widely spaced flaking rolls, and tempered for 24 hours. The bumped kernels are then finally puffed and toasted in a toasting oven for 30-45 seconds. The resulting product is a highly expanded cereal product with a tender, crisp structure.
Given the number and complexity of steps in the typical oven puffing process, it would be desirable to produce a crisp rice suitable for use in a breakfast cereal or for use in snacks and confections by a simple extrusion puffing method in which uncooked rice flour is used as the starting ingredient.
Although extrusion-cooking of cereal flour mixtures to make puffed cereal products is well established in the cereal making art, difficulties have been observed when cereal flour mixtures containing high levels of uncooked rice flour have been extrusion-cooked. Specifically, we have found that rice flour mixtures having a rice flour content above about 50% may be extruded satisfactorily in a high pressure single screw extruder having a water cooled screw. However, after a period of operation varying from a few minutes to a few days, the output of the extruder may suddenly and unexpectedly drop, totally disrupting production of the product. Upon removing the screw from the extruder barrel after these stoppages, a hard, glassy substance is found to be adhering to the screw and filling the channels between adjacent screw flights, thereby blocking the flow of cereal flour mixture through the extruder. The exact reason for this "screw wrap" problem, which appears after a variable period of stable operation, is unknown. Other flours such as corn flour, wheat flour, and oat flour, when extrusion-cooked under substantially the same conditions, do not experience such severe screw wrap problems.
A time consuming-process of removing the glassy substance from the screw is required before cereal production can be resumed. This task can be a source of considerable production down-time. As a result, the screw wrap problem presents a significant obstacle to the economics and feasibility of the extrusion method for making crisp rice.
It is therefore an object of the present invention to provide an extrusion method for making a crisp rice product which avoids the screw wrap problem.
It is also an object of the present invention to provide an extrusion method for making a crisp rice product from rice flour that is organoleptically comparable to crisp rice produced by oven puffing of whole grain rice.